The present invention relates to a cost effective process for producing acetylene-terminated resins from halogen-terminated oligomers prepared by an Ullmann condensation in 2,4,6-collidine with an excess of cuprous oxide.
Acetylene terminated resins are being considered as substitutes for epoxy resins in certain composites because they exhibit better resistance to moisture than their epoxy counterparts. One drawback of these resins, however, is that they have been relatively difficult to synthesize and expensive to produce. Using prior synthetic approaches it has been difficult to control the average oligomer length in order to maintain a reproducible and acceptable balance between processability and mechanical properties. In addition total product yields have been difficult to reproduce and maximize. Consequently, prior syntheses have not been entirely satisfactory for producing these oligomers on a commercial scale.
The preparation of acetylene-terminated sulphones by an Ullman-type condensation is described in U.S. Pat. No. 4,356,325 to Harrison et al (1982). There, a sulfonyldiphenol, such as 4,4'-sulfonyldiphenol, is reacted with meta- or para-dibromobenzene in the presence of a potassium base, a copper salt, and a pyridine solvent to produce a bromine-terminated oligomer which is converted to the acetylene-terminated oligomer by reacting with a substituted terminal acetylene compound. This synthesis has not been entirely satisfactory, however, because the yield of the bromine-terminated oligomers is low and the oligomer chain length cannot be adequately controlled by varying the mole ratio of the sulfonyldiphenol to the dibromobenzene. Consequently, it is difficult to obtain oligomers having predetermined processing characteristics and mechanical properties by this synthesis
R. Bacon and G. Stewart, "Metal Ions and Complexes in Organic Reactions, Part IV, Copper-promoted Preparation of Diaryl Ethers and Competing Hydrogen-transfer Processes", J. Chem. Soc., 4953 (1965) discloses the use of cuprous oxide in combination with 2,4,6-collidine in the condensations of phenols (including a diphenol) and monobrominated aromatic compounds to produce aryl ethers. However, the paper notes a competing reaction in which bromine is replaced by hydrogen in the reactants which, on its face, would discourage using the subject catalyst-solvent system to produce oligomers in which terminal bromine atoms are required. Furthermore, the paper does not address the synthesis of oligomers by using dibromo compounds in the reaction, in which other catalyst solvent systems have failed to provide reproducible results and high yields.
Thus, there is a need for a commercially suitable process for producing halogen-terminated oligomers for use in forming acetylene terminated oligomers which provides a means for tailoring the chain length of the oligomers and providing the oligomers in high yields.